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SyncMaster 931BW no power

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    #1

    SyncMaster 931BW no power

    Hi all!
    I'm new to this forum and I want to say that it was a great help for me with couple of old LCD's, and all I had to do is to search!

    Now to the topic, I followed the troubleshoot here with no luck
    My power board is of a different model PWI1704SV rev1.3
    I connected just the power board without anything else and got a 4.9-4.95V on the 5.1V pins, 0V on the 13V pin and also on all the other pins.
    So the problem is with the power board and I thought to myself that it's a good thing and I can fix that
    The electrolytic caps seemed to be OK but just in case I replaced all of them except the C101 100mf 450V and two 22mF 50V(didn't have any ),
    but i checked their capacity(my cheep voltmeter has a capacitor tester up to 200mF) and got 18mF which is good.
    Checked the voltage on the C101 and got 314V which is OK (I live in Israel and we got 230V)

    I followed Bill's excellent instructions and got to the FSDM0565R Power Switch(different from the original post I followed),
    I measured the voltage between the Vcc and GND(pins 2 and 3 from this datasheet) and it varies from ~11V to 14V constantly.
    According to Bill I need to change the start-up cap which in my case is C104(I think), so I did but it didn't help
    I also tried to replace the power switch with another one just like it which I salvaged from another Samsung board but I got the same readings...
    So now I'm stuck...

    I attached pictures of the board with some markings, hope you can help me
    Attached Files
    Last edited by BrAvE_26; 11-23-2012, 05:13 AM.
    Tags: None
    #2
    Re: SyncMaster 931BW no power

    Its a great write up but you dont actually say what the problem is.
    Please can you start from plugging it in to the final fault stage and tell us what happens.
    What does the power led do what does the screen do any sounds clicks, wheezes etc - have a working video source connected whilst doing this.
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment

      #3
      Re: SyncMaster 931BW no power

      LOL sorry I thought the title says it all
      I have no power what so ever, no flickering, no power led indication, no sounds just dead.
      Didn't try to connect it to a video source.

      Comment

        #4
        Re: SyncMaster 931BW no power

        Did you at some point do the voltage tests on the power supply>main connector when it was all connected up?
        Please upload pictures using attachment function when ask for help on the repair
        http://www.badcaps.net/forum/showthread.php?t=39740

        Comment

          #5
          Re: SyncMaster 931BW no power

          Yep, got the same results with the new capacitors.
          But I didn't try to connect it all up again after I replaced the DM0565 power switch

          Comment

            #6
            Re: SyncMaster 931BW no power

            Ok can you try with it all connected up and can you also post a well lit close up picture of the soldering on the DM0565.
            It may also be a good idea to look at all the solder joints with a magnifying glass as some look a bit odd R181 in bottom left C202 the righthand side joint c30 right hand joint - maybe its just the pictures - only you can check.
            Please upload pictures using attachment function when ask for help on the repair
            http://www.badcaps.net/forum/showthread.php?t=39740

            Comment

              #7
              Re: SyncMaster 931BW no power

              Also check you got all the caps the right way round and can you tell us what make/series you used.
              Please upload pictures using attachment function when ask for help on the repair
              http://www.badcaps.net/forum/showthread.php?t=39740

              Comment

                #8
                Re: SyncMaster 931BW no power

                D282 and D283 at the top of the Board should be checked for short circuit,as these regularly give problems.

                Comment

                  #9
                  Re: SyncMaster 931BW no power

                  Got it, I'm going to check everything out and post back.

                  Comment

                    #10
                    Re: SyncMaster 931BW no power

                    Checked the solder joints, seems OK.
                    Checked all the caps for the right position and make/series:
                    1000mF, 470mF, 330mF all are Nichicon make, series PET
                    As for the diodes, which numbered 202 and 203(sorry for the poor picture from before),
                    when I connect the black lead to the cathode and red to the anode I get a read of 167 Ohms but according to this I should get 1K +-25%
                    so I don't really know if it's OK or not....
                    Connected it all up and still nothing....
                    Attached Files

                    Comment

                      #11
                      Re: SyncMaster 931BW no power

                      Originally posted by BrAvE_26 View Post
                      when I connect the black lead to the cathode and red to the anode I get a read of 167 Ohms but according to this I should get 1K +-25%
                      so I don't really know if it's OK or not....
                      .


                      Ok that is only half the diode test what do you get when you reverse the leads. Are both diodes reading the same? If in doubt they will have to be tested off the board.

                      Nichicon caps are usually ok unless you bought them on ebay.

                      I am still not sure about the soldering on the power control it "looks" as though the joints could be touching?
                      Please upload pictures using attachment function when ask for help on the repair
                      http://www.badcaps.net/forum/showthread.php?t=39740

                      Comment

                        #12
                        Re: SyncMaster 931BW no power

                        Both diodes read the same 167, and when I reverse the leads I get 1770 on both diodes.
                        Checked the joints on the DM0565 for short circuit and they aren't touching....
                        What should I do now?

                        Comment

                          #13
                          Re: SyncMaster 931BW no power

                          Remove the two diodes and check off board - one way should be offscale - at the moment it looks like they are bad.
                          Please upload pictures using attachment function when ask for help on the repair
                          http://www.badcaps.net/forum/showthread.php?t=39740

                          Comment

                            #14
                            Re: SyncMaster 931BW no power

                            Removed the diodes, one way goes of scale the other is 170 on the both of them.
                            Last edited by BrAvE_26; 11-23-2012, 06:29 PM.

                            Comment

                              #15
                              Re: SyncMaster 931BW no power

                              Thats a pity looks like they are ok - we will have to think of something else
                              Please upload pictures using attachment function when ask for help on the repair
                              http://www.badcaps.net/forum/showthread.php?t=39740

                              Comment

                                #16
                                Re: SyncMaster 931BW no power

                                The fluctuating voltage on the SMPS IC is either

                                a) bad SMPS IC
                                b) bad startup cap
                                c) something shorted and loading down the SMPS

                                Since you already replaced the SMPS IC and startup cap, the next step is to check all your diodes (including the zeners and ones mounted on any heatsinks) to see if any are shorted.
                                Last edited by retiredcaps; 11-24-2012, 04:03 PM.
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                                  #17
                                  Re: SyncMaster 931BW no power

                                  Checked all the diodes and zeners and what do you know.... the D201 the one with the heat-sink is shorted I think...
                                  It's model is MBR10150CT and all the pin combinations short out(1-2,1-3,2-3)
                                  so is this my little problem!?

                                  Comment

                                    #18
                                    Re: SyncMaster 931BW no power

                                    It sounds like it. Usually you'll hear a slight ticking sound when this happens though...
                                    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                                    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                                    Comment

                                      #19
                                      Re: SyncMaster 931BW no power

                                      I found an MBR10150CT on a broken board and it doesn't short out!!!
                                      I'm going to try and replace mine and see if it works and post back!

                                      YES YES YES!
                                      It works!!!! THANK you all never could I have done it without your help!


                                      PS.
                                      I hear a very very faint high pitched sound from the power board, should I be concerned?
                                      Last edited by BrAvE_26; 11-24-2012, 08:46 PM.

                                      Comment

                                        #20
                                        Re: SyncMaster 931BW no power

                                        Originally posted by BrAvE_26 View Post
                                        I hear a very very faint high pitched sound from the power board, should I be concerned?
                                        It could be the little caps that you did not change?
                                        --- begin sig file ---

                                        If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                                        We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                                        Please do not post inline and offsite as they slow down the loading of pages.

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                                        Comment

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